Differential DNA-replication and DNA-catabolism occurring at least once in the cell cycle of normal diploid and aneuploid cells will be investigated. The possibility that transient DNA-amplification is under controls which are separable from replication for cell division will be tested. The idea that this periodically synthesized DNA represents amplified extra-chromosomal nucleotide sequences which are not copied in the classical semiconservative manner will be tested. The possibility that these are ribosomal-DNA and repetitious-DNA sequences made by way of an RNA intermediate requiring the presence of an RNA-dependent-DNA-polymerase will be pursued, and the relationship of this phenomenon to periodic increases in RNA and enzyme synthesis and to timekeeping mechanisms in dividing and differentiating cells will be explored.